DISTRIBUTED DEFORMATION DUE TO COUPLING ACROSS A SUBDUCTION THRUST - MECHANISM OF YOUNG TECTONIC ROTATION WITHIN THE SOUTH WANGANUI BASIN, NEW-ZEALAND

Paleomagnetic data from Pliocene sedimentary strata in the south Wanga nui basin, New Zealand, document clockwise tectonic rotation west of a nd increasing toward the main zone of deformation (axial tectonic belt ) associated with the Australia-Pacific plate boundary zone in the Nor th Island of New Zealand. Measured rotation with respect to the Austra lian plate increases from 1.4 degrees +/- 3.9 degrees 80 km west of th e axial tectonic belt to 6.5 degrees +/- 2.0 degrees and 13.2 degrees +/- 3.1 degrees at 45 km and 20 km west of the axial tectonic belt, re spectively. These measurements indicate that (1) deformation associate d with plate convergence occurs across a wide region up to 270 km west of the Hikurangi Trench, and (2) in the past 2.5 m.y. at least 30 km of transcurrent motion and 10 km of shortening at the plate boundary h ave been accommodated within the south Wanganui basin by distributed s hear west of the plate boundary zone proper. The data support a model suggesting that the Wanganui basin is a lithospheric flexure basin dri ven by high friction at the plate interface. This strain in the south Wanganui basin and inferred high friction across the plate interface a t the basin's eastern margin have occurred since 2.5 Ma.